Electric vehicles and hybrid vehicles have increasingly been marketed with consideration to the environment and to improve fuel efficiency. In these vehicles, when a starter, which consumes a large current intermittently during use, is driven, a battery voltage temporarily drops. An automotive capacitor device is employed as an auxiliary power supply for supplying sufficient power to a load during this temporal drop of the battery voltage or for supplying power to a vehicle control system at occurrence of battery abnormality.
FIG. 7 is a circuit block diagram of conventional capacitor device 70. In capacitor device 70, plural capacitors storing battery power of the main power supply constitute capacitor unit 71. Charge circuit 72 for charging capacitor unit 71 is connected to capacitor unit 71. Control circuit 73 controls charge circuit 72.
Control circuit 73 charges capacitor unit 71 up to a full-charge voltage. When control circuit 73 detects a voltage drop of the main power supply based on a voltage signal from main power voltage detecting circuit 74, control circuit 73 turns on switch 75 to supply power of capacitor unit 71 to the load.
Japanese Patent Laid-Open Publication No. 2006-340505 discloses a conventional capacitor device similar to capacitor device 70.
In conventional capacitor device 70, at low temperatures, since a capacitance of a capacitor decreases and an internal resistance increases, the stored power decreases, thus degrading storage performance. On the other hand, at high temperatures, a storage performance of the capacitor improves at high temperatures, but the capacitor tends to deteriorate due to an overcharge applied to the capacitor.